The present invention relates to subterranean drilling operations. More particularly, the present invention relates to methods of drilling a well bore in a subterranean formation comprising placing a self-degrading kickoff plug or the like in the well bore.
During drilling of a well for production of oil, gas, or other fluids, it may be desirable to perform directional drilling, which may result in drilling of a deviated well bore. Directional drilling operations may be conducted for a variety of reasons, including, but not limited to, evading obstructions (e.g., drilling equipment that may have become stuck in the original well bore), drilling multiple wells from a single vertical well bore, or increasing production by increasing flow from adjacent subterranean formations.
Directional drilling operations may involve the setting of a kickoff plug, or the like, in a primary well bore. A kickoff plug may have a length ranging from about 50 to about 500 feet, and may comprise a cement composition. The kickoff plug typically is set in the well bore by lowering a drillstring or an open-ended tubing string to the desired depth and pumping a cement composition into the well bore. The cement composition may set to form a plug. After the cement plug has been formed, a drillstring may be used to reinitiate drilling operations. The drillstring and drill bit intentionally may be contacted with the plug, so as to thereby deflect the drill string and change the direction in which subsequent drilling proceeds.
The use of conventional kickoff plugs may be problematic, for a variety of reasons. Conventional kickoff plugs may be difficult to remove from the primary well bore, and may block the well bore and/or impair production of hydrocarbons from the subterranean formation. Even where removal of the kickoff plug from the well bore is possible, the removal procedure may require additional trips into the well bore, adding cost to the drilling operation. Furthermore, in cases in which a mechanical kickoff plug assembly is used, retrieving the kickoff plug by pulling it back up through the well bore may be problematic, because the well bore may lack sufficient space through which to pull the kickoff plug without damaging upper portions of the well bore and/or casing strings set therein.
Conventional approaches to solving these problems have included, inter alia, the use of a salt plug which, once used, can be dissolved by the introduction of an acidic solution into the well bore. However, significant drawbacks may be associated with this approach, including, but not limited to, environmental and occupational safety risks that may result from the use of large quantities of the acidic solution, the risk that a portion of the acidic solution may escape into other regions of the subterranean formation, and the delay of waiting for the acidic solution to dissolve the plug.
Another conventional approach involves drilling through the kickoff plug. However, this approach may require the use of other drilling equipment (e.g., drilling strings capable of producing a greater force, and a stabilizer assembly to keep the drill string from being deflected by the plug) that may further complicate the drilling operation and/or risk damage to the well bore.